U.S. patent application number 12/375499 was filed with the patent office on 2009-10-08 for multi-hop network topology system and method.
Invention is credited to Mo-Han Fong, Nimal Gamini Senarath, David Steer, Wen Tong, Derek Yu, Hang Zhang, Peiying Zhu.
Application Number | 20090252065 12/375499 |
Document ID | / |
Family ID | 38981094 |
Filed Date | 2009-10-08 |
United States Patent
Application |
20090252065 |
Kind Code |
A1 |
Zhang; Hang ; et
al. |
October 8, 2009 |
MULTI-HOP NETWORK TOPOLOGY SYSTEM AND METHOD
Abstract
A wireless communication system and method for a network having
a tree topology. An initial path from a base station to an end
relay node is selected. The path selection includes an active
communication path and a redundant communication path. The path
selection is based on at least one policy factor. The at least one
policy factor is monitored and the path is updated based on a
change to the monitored at least one policy factor.
Inventors: |
Zhang; Hang; (Nepean,
CA) ; Zhu; Peiying; (Kanata, CA) ; Tong;
Wen; (Ottawa, CA) ; Fong; Mo-Han; (L'Original,
CA) ; Senarath; Nimal Gamini; (Nepean, CA) ;
Steer; David; (Nepean, CA) ; Yu; Derek;
(Kanata, CA) |
Correspondence
Address: |
CHRISTOPHER & WEISBERG, P.A.
200 EAST LAS OLAS BOULEVARD, SUITE 2040
FORT LAUDERDALE
FL
33301
US
|
Family ID: |
38981094 |
Appl. No.: |
12/375499 |
Filed: |
July 27, 2007 |
PCT Filed: |
July 27, 2007 |
PCT NO: |
PCT/CA07/01328 |
371 Date: |
January 28, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60820692 |
Jul 28, 2006 |
|
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|
Current U.S.
Class: |
370/256 ;
370/338 |
Current CPC
Class: |
H04L 45/308 20130101;
H04L 41/0856 20130101; H04W 40/248 20130101; H04L 45/28 20130101;
H04L 45/122 20130101; H04L 45/22 20130101; H04B 7/2606 20130101;
H04L 41/082 20130101; H04W 40/04 20130101; H04W 40/22 20130101;
H04W 40/12 20130101; H04L 41/5025 20130101 |
Class at
Publication: |
370/256 ;
370/338 |
International
Class: |
H04L 12/28 20060101
H04L012/28 |
Claims
1. A wireless communication method for a network having a tree
topology, the method comprising: selecting an initial path from a
base station to an end relay node, the path selection including an
active communication path and a redundant communication path, the
path selection being based on at least one policy factor;
monitoring the at least one policy factor; and updating the path
based on a change to the monitored at least one policy factor.
2. The method of claim 1, wherein the at least one policy factors
include one or more of a number of hops, link quality and path
capacity room.
3. The method of claim 1, wherein the network is an IEEE 802.16j
network.
4. The method of claim 1, wherein the active communication path and
the redundant communication path are defined as an equivalent path
from the base station to the end relay node.
5. The method of claim 1, wherein the active communication path and
the redundant communication path are defined as a primary path and
assistant path, respectively, from the base station to the end
relay node.
6. The method of claim 1, further comprising using a relay node
preamble to measure at least one of the policy factors.
7. The method of claim 6, wherein measuring at least one of the
policy factors includes: randomly selecting a monitoring cycle from
a monitoring cycle selection base, the monitoring cycle selection
base comprising a plurality of preamble cycles; stopping
transmission of the relay node preamble during the selected
monitoring cycle; and transmitting relay node preambles during the
remaining preamble cycles
8. The method of claim 1, wherein the path selection is distributed
such that path selection is determined at least in part by a relay
node.
9. The method of claim 1, wherein the path selection is centralized
such that path selection is determined by a base station.
10. The method of claim 1, further comprising: storing a topology
table corresponding to a local topology; detecting a change in the
local topology; and requesting a path selection update; the path
selection comprising the active communication path and the
redundant communication path.
11. The method of claim 11, wherein an architecture of the topology
is a hierarchical topology, the hierarchical topology including a
master relay node supporting a group of relay nodes.
12. A method for a relay node to use a relay node preamble to
evaluate a wireless communication radio environment, the method
comprising: randomly selecting a monitoring cycle from a monitoring
cycle selection base, the monitoring cycle selection base
comprising a plurality of preamble cycles; stopping transmission of
the relay node preamble during the selected monitoring cycle; and
transmitting relay node preambles during the remaining preamble
cycles.
13. The method of claim 12, wherein the wireless communication
radio environment is an IEEE 802.16j wireless communication
network.
14. A wireless communication system having a tree topology, the
system comprising: a base station; a first relay node in
communication with the base station; and a second relay node in
direct communication with at least one of the base station and the
first relay node, an active communication path being established
from the base station to the second relay node and a redundant
communication path being established from the base station to the
second relay node, the redundant communication path being different
than the active communication path and at least one of the active
communication path and the redundant communication path including
the first relay node.
15. The system of claim 14, wherein the network is an IEEE 802.16j
network.
16. The system of claim 14, wherein the active communication path
and the redundant communication path are defined as an equivalent
path from the base station to the second relay node.
17. The system of claim 14, wherein the active communication path
and the redundant communication path are defined as a primary path
and assistant path, respectively, from the base station to the
second relay node.
18. The system of claim 14, further comprising using a relay node
preamble to measure a radio environment, the measured radio
environment being used to establish the active and redundant
communication paths.
19. The system of claim 18, wherein the first and second relay
nodes: each randomly select a monitoring cycle from a monitoring
cycle selection base, the monitoring cycle selection base
comprising a plurality of preamble cycles; stop transmission of the
relay node preamble during their selected monitoring cycle; and
transmit relay node preambles during the remaining preamble
cycles.
20. The system of claim 14, wherein the active and redundant
communication paths are selected by the second relay node.
21. The system of claim 14, wherein the base station includes a
storage device storing a topology table corresponding to a local
topology, and wherein the base station operates to detect a change
in the local topology and requests a path selection update, the
path selection comprising the active communication path and the
redundant communication path.
22. The system of claim 14, wherein an architecture of the topology
is a hierarchical topology, and wherein at least one of the first
relay node and the second relay node is a master relay node
supporting a group of relay nodes.
23. The system according to claim 14, wherein the active path
selection and the redundant path selection is based on at least one
policy factor.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method and system for
wireless communication and in particular to a method and system for
wireless communication using relay nodes.
BACKGROUND OF THE INVENTION
[0002] As the demand for high speed broadband networking over
wireless communication links increases, so too does the demand for
different types of networks that can accommodate high speed
wireless networking. For example, the deployment of IEEE 802.11
wireless networks in homes and business to create Internet access
"hot spots" has become prevalent in today's society. However, these
IEEE 802.11-based networks are limited in bandwidth as well as
distance. For example, maximum typical throughput from a user
device to a wireless access point is 54 MB/sec. at a range of only
a hundred meters or so. In contrast, while wireless range can be
extended through other technologies such as cellular technology,
data throughput using current cellular technologies is limited to a
few MB/sec. Put simply, as the distance from the base station
increase, the need for higher transmission power increases and the
maximum data rate typically decreases. As a result, there is a need
to support high speed wireless connectivity beyond a short distance
such as within a home or office.
[0003] As a result of the demand for longer range wireless
networking, the IEEE 802.16 standard was developed. The IEEE 802.16
standard is often referred to as WiMAX or less commonly as
WirelessMAN or the Air Interface Standard. This standard provides a
specification for broadband wireless metropolitan access networks
("MAN"s) that use a point-to-multipoint architecture. Such
communications can be implemented, for example, using orthogonal
frequency division multiplexing ("OFDM") communication. OFDM
communication uses a multi-carrier technique that distributes the
data over a number of carriers that are spaced apart at precise
frequencies. This spacing provides the "orthogonality" that
prevents the demodulators from seeing frequencies other than their
own.
[0004] The 802.16 standard supports high bit rates in both the
uplink to and downlink from a base station up to a distance of 30
miles to handle such services as VoIP, IP connectivity and other
voice and data formats. Expected data throughput for a typical
WiMAX network is 45 MBits/sec. per channel. The 802.16e standard
defines a media access control ("MAC") layer that supports multiple
physical layer specifications customized for the frequency band of
use and their associated regulations. However, the 802.16e standard
does not provide support for multi-hop networks that use relay
nodes.
[0005] 802.16 networks, such as 802.16j networks, can be deployed
as multi-hop networks from the subscriber equipment to the carrier
base station. In other words, in multi-hop networks, the subscriber
device can communicate with the base station directly or through
one or more intermediate devices.
[0006] The complexity involved in supporting multi-hop networks in
a robust manner necessarily involves sophisticated control layer
protocols. Such protocols do not exist. For example, as noted
above, the IEEE 802.16e standard does not support multi-hop
networks. The IEEE 802.16j standard for supporting multi-hop
networks has been proposed, but the standard supports only a
tree-based topology and does not provide good arrangements or
methods for advanced topology support such as active and redundant
path selection, i.e., path diversity, topology learning and
congestion control for wireless communication from the mobile
station to the supporting base station. As such, relay-based
networks implemented under the existing IEEE 802.16j standard do
not provide a reliable communication environment that can easily
react to congestion and topology changes whether through the
addition or subtraction of a relay node as part a normal business
process or as a result of a failure or error condition within the
network.
[0007] It is therefore desirable to have method and system that
provides an arrangement to support such topology-related aspects of
wireless networks that include relay stations. Such
topology-related aspects include congestion control, topology
learning and path diversity from the mobile station to the base
station via relay nodes (also referred to herein as "relay
stations"), including but not limited to those operating in
accordance with the IEEE 802.16 standards.
[0008] Current IEEE 802.16 mobile stations are typically arranged
to communicate using the IEEE 802.16e standard. As such, in order
to maintain backward compatibility, relay stations configured to be
serving stations (deliver/collect traffic to/from mobile stations)
are arranged to transmit an 802.16e preamble to facilitate cell
selection by the mobile station. However, a problem will arise in
an environment in which relay stations are implemented in a
wireless network that is arranged to support the desired
topology-related aspects described above. For example, in order to
support removal and addition of new relay stations, existing relay
stations would need to monitor their operating environments to
synchronize operation for path reselection. This would be done via
monitoring preamble transmissions from neighboring relay stations.
As such, a single radio relay node wanting to monitor preambles to
support topology-related changes would stop its own IEEE 802.16e
preamble transmission thereby adversely impacting the normal
operation of supported mobile stations.
[0009] It is therefore also desirable to have a wireless
communication network arrangement that allows relay nodes to both
transmit and monitor preambles to support mobile stations as well
as topology-related changes.
SUMMARY OF THE INVENTION
[0010] The present invention advantageously provides a method and
system for supporting topology changes in wireless communication
networks, including but not limited to those operating under the
IEEE 802.16j standard.
[0011] In accordance with one aspect, the present invention
provides a wireless communication method for a network having a
tree topology. An initial path from a base station to an end relay
node is selected. The path selection includes an active
communication path and a redundant communication path. The path
selection is based on at least one policy factor. The at least one
policy factor is monitored and the path is updated based on a
change to the monitored at least one policy factor. Optionally, the
network is an IEEE 802.16j network.
[0012] In accordance with another aspect, the present invention
provides a wireless communication system having a tree topology in
which there is a base station. A first relay node is in
communication with the base station. A second relay node is in
direct communication with at least one of the base station and the
first relay node. An active communication path is established from
the base station to the second relay node and a redundant
communication path is established from the base station to the
second relay node. The redundant communication path is different
than the active communication path. At least one of the active
communication path and the redundant communication path include the
first relay node.
[0013] In accordance with still another aspect, the present
invention provides a method for using a relay node preamble to
evaluate a wireless communication radio environment. A monitoring
cycle is randomly selecting from a monitoring cycle selection base
in which the monitoring cycle selection base has a plurality of
preamble cycles. Transmission of the relay node preamble is stopped
by the relay node during the selected monitoring cycle. Relay node
preambles are transmitted by the relay node during the remaining
preamble cycles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] A more complete understanding of the present invention, and
the attendant advantages and features thereof, will be more readily
understood by reference to the following detailed description when
considered in conjunction with the accompanying drawings
wherein:
[0015] FIG. 1 is a diagram of an embodiment of a system constructed
in accordance with the principles of the present invention;
[0016] FIG. 2 is a block diagram of an exemplary base station
constructed in accordance with the principles of the present
invention;
[0017] FIG. 3 is a block diagram of an exemplary mobile station
constructed in accordance with the principles of the present
invention;
[0018] FIG. 4 is a block diagram of an exemplary OFDM architecture
constructed in accordance with the principles of the present
invention;
[0019] FIG. 5 is a block diagram of the flow of received signal
processing in accordance with the principles of the present
invention;
[0020] FIG. 6 is a diagram of an exemplary scattering of pilot
symbols among available sub-carriers;
[0021] FIG. 7 is a block diagram of an exemplary flat network
architecture constructed in accordance with the principles of the
present invention;
[0022] FIG. 8 is a block diagram of an exemplary hierarchical
network architecture constructed in accordance with the principles
of the present invention;
[0023] FIG. 9 is a block diagram of an exemplary network
communication path constructed in accordance with the principles of
the present invention;
[0024] FIG 10 is a block diagram showing a communication path
definition constructed in accordance with the principles of the
present invention;
[0025] FIG. 11 is a block diagram showing the equivalent path
definition of the path shown in FIG. 10;
[0026] FIG. 12 is a block diagram of a primary/assistant path relay
node topology constructed in accordance with the principles of the
present invention;
[0027] FIG. 13 is a diagram showing an exemplary relay node
preamble transmission timing arrangement constructed in accordance
with the principles of the present invention; and
[0028] FIG. 14 is a diagram of path capacity through an exemplary
network path.
DETAILED DESCRIPTION OF THE INVENTION
[0029] It is noted that various multi-hop communication schemes are
described herein in accordance with the present invention. While
described in the context of the Institute of Electrical and
Electronics Engineers ("IEEE") 802.16 standards, one of ordinary
skill in the art will appreciate that the broader inventions
described herein are not limited in this regard and merely for
exemplary and explanatory purposes.
[0030] According to the present invention, various media access
control ("MAC") layer designs for downlink communications between a
base station ("BS") and a relay station ("RS") and between a RS and
RS are described. One of ordinary skill in the art will appreciate
that the invention described herein is not limited solely to use
with downlink communications but is equally applicable to uplink
communications as well, for example between a mobile station ("MS")
and RS, a RS and RS, and a RS and BS.
[0031] According to one embodiment of the invention a Relay Station
MAC (R-MAC) layer is introduced. According to another embodiment
the existing IEEE 802.16e MAC is modified to implement and support
the features and functions described herein.
[0032] Referring now to the drawing figures in which like reference
designators refer to like elements, there is shown in FIG. 1, a
system constructed in accordance with the principles of the present
invention and designated generally as "10." System 10 includes base
stations 12, relay nodes 14 and mobile stations 16. Base stations
12 communicate with one another and with external networks, such as
the Internet (not shown), via carrier network 18. Base stations 12
engage in wireless communication with relay nodes 14 and/or mobile
stations 16. Similarly, mobile stations 16 engage in wireless
communication with relay nodes 14 and/or base stations 12.
[0033] Base station 12 can be any base station arranged to
wirelessly communicate with relay nodes 14 and/or mobile stations
16. Base stations 12 include the hardware and software used to
implement the functions described herein to support the MAC control
plane functions. Base stations 12 include a central processing
unit, transmitter, receiver, I/O devices and storage such as
volatile and nonvolatile memory as may be needed to implement the
functions described herein. Base stations 12 are described in
additional detail below.
[0034] Mobile stations 16, also described in detail below, can be
any mobile station including but not limited to a computing device
equipped for wireless communication, cell phone, wireless personal
digital assistant ("PDA") and the like. Mobile stations 16 also
include the hardware and software suitable to support the MAC
control plane functions needed to engage in wireless communication
with base station 12 either directly or via one or more relay nodes
14. Such hardware can include a receiver, transmitter, central
processing unit, storage in the form of volatile and nonvolatile
memory, input/output devices, etc.
[0035] Relay node 14 is used to facilitate wireless communication
between mobile station and base station 12 in the uplink (mobile
station 16 to base station 12) and/or the downlink (base station 12
to mobile station 16). A relay node 14 configured in accordance
with the principles of the present invention includes a central
processing unit, storage in the form of volatile and/or nonvolatile
memory, transmitter, receiver, input/output devices and the like.
Relay node 14 also includes software to implement the MAC control
functions described herein. Of note, the arrangement shown in FIG.
1 is general in nature and other specific communication embodiments
constructed in accordance with the principles of the present
invention are contemplated.
[0036] Although not shown, system 10 includes a base station
controller ("BSC") or access service network ("ASN") gateway that
controls wireless communications within multiple cells, which are
served by corresponding base stations ("BS") 12. In general, each
base station 12 facilitates communications using, for example OFDM,
directly with mobile stations 16 or via one or more relay nodes 14,
of which at least one of which is within the cell 12 associated
with the corresponding base station 12. The movement of the mobile
stations 16 (and mobile relay nodes 14) in relation to the base
stations 12 results in significant fluctuation in channel
conditions. It is contemplated that the base stations 12, relay
nodes 14 and mobile stations 16 may include multiple antennas in a
multiple input multiple output ("MIMO") arrangement to provide
spatial diversity for communications.
[0037] A high level overview of the mobile stations 16 and base
stations 12 of the present invention is provided prior to delving
into the structural and functional details of the preferred
embodiments. It is understood that relay nodes 14 can incorporate
those structural and functional aspects described herein with
respect to base stations 12 and mobile stations 16 as may be needed
to perform the functions described herein.
[0038] With reference to FIG. 2, a base station 12 configured
according to one embodiment of the present invention is
illustrated. The base station 12 generally includes a control
system 20 such as a central processing unit, a baseband processor
22, transmit circuitry 24, receive circuitry 26, multiple antennas
28, and a network interface 30. The receive circuitry 26 receives
radio frequency signals bearing information from one or more remote
transmitters provided by mobile stations 16 (illustrated in FIG.
3). Preferably, a low noise amplifier and a filter (not shown)
cooperate to amplify and remove out-of-band interference from the
signal for processing. Down conversion and digitization circuitry
(not shown) then down converts the filtered, received signal to an
intermediate or baseband frequency signal, which is then digitized
into one or more digital streams.
[0039] The baseband processor 22 processes the digitized received
signal to extract the information or data bits conveyed in the
received signal. This processing typically comprises demodulation,
decoding, and error correction operations. As such, the baseband
processor 22 is generally implemented in one or more digital signal
processors ("DSPs") or application-specific integrated circuits
("ASICs"). The received information is then sent across a wireless
network via the network interface 30 or transmitted to another
mobile station 16 serviced by the base station 12.
[0040] On the transmit side, the baseband processor 22 receives
digitized data, which may represent voice, data, or control
information, from the network interface 30 under the control of
control system 20, and encodes the data for transmission. The
encoded data is output to the transmit circuitry 24, where it is
modulated by a carrier signal having a desired transmit frequency
or frequencies. A power amplifier (not shown) amplifies the
modulated carrier signal to a level appropriate for transmission,
and delivers the modulated carrier signal to the antennas 28
through a matching network (not shown). Modulation and processing
details are described in greater detail below.
[0041] With reference to FIG. 3, a mobile station 16 configured
according to one embodiment of the present invention is described.
Similar to base station 12, a mobile station 16 constructed in
accordance with the principles of the present invention includes a
control system 32, a baseband processor 34, transmit circuitry 36,
receive circuitry 38, multiple antennas 40, and user interface
circuitry 42. The receive circuitry 38 receives radio frequency
signals bearing information from one or more base stations 12.
Preferably, a low noise amplifier and a filter (not shown)
cooperate to amplify and remove out-of-band interference from the
signal for processing. Down conversion and digitization circuitry
(not shown) then down convert the filtered, received signal to an
intermediate or baseband frequency signal, which is then digitized
into one or more digital streams.
[0042] The baseband processor 34 processes the digitized received
signal to extract the information or data bits conveyed in the
received signal. This processing typically comprises demodulation,
decoding, and error correction operations, as will be discussed on
greater detail below. The baseband processor 34 is generally
implemented in one or more digital signal processors ("DSPs") and
application specific integrated circuits ("ASICs").
[0043] With respect to transmission, the baseband processor 34
receives digitized data, which may represent voice, data, or
control information, from the control system 32, which it encodes
for transmission. The encoded data is output to the transmit
circuitry 36, where it is used by a modulator to modulate a carrier
signal that is at a desired transmit frequency or frequencies. A
power amplifier (not shown) amplifies the modulated carrier signal
to a level appropriate for transmission, and delivers the modulated
carrier signal to the antennas 40 through a matching network (not
shown). Various modulation and processing techniques available to
those skilled in the art are applicable to the present
invention.
[0044] In OFDM modulation, the transmission band is divided into
multiple, orthogonal carrier waves. Each carrier wave is modulated
according to the digital data to be transmitted. Because OFDM
divides the transmission band into multiple carriers, the bandwidth
per carrier decreases and the modulation time per carrier
increases. Since the multiple carriers are transmitted in parallel,
the transmission rate for the digital data, or symbols, on any
given carrier is lower than when a single carrier is used.
[0045] OFDM modulation is implemented, for example, through the
performance of an Inverse Fast Fourier Transform ("IFFT") on the
information to be transmitted. For demodulation, a Fast Fourier
Transform ("FFT") on the received signal is performed to recover
the transmitted information. In practice, the IFFT and FFT are
provided by digital signal processing carrying out an Inverse
Discrete Fourier Transform (IDFT) and Discrete Fourier Transform
("DFT"), respectively. Accordingly, the characterizing feature of
OFDM modulation is that orthogonal carrier waves are generated for
multiple bands within a transmission channel. The modulated signals
are digital signals having a relatively low transmission rate and
capable of staying within their respective bands. The individual
carrier waves are not modulated directly by the digital signals.
Instead, all carrier waves are modulated at once by IFFT
processing.
[0046] In one embodiment, OFDM is used for at least the downlink
transmission from the base stations 12 to the mobile stations 16
via relay nodes 14. Each base station 12 is equipped with n
transmit antennas 28, and each mobile station 16 is equipped with m
receive antennas 40. Relay nodes 14 can include multiple transmit
and receive antennas as well. Notably, the respective antennas can
be used for reception and transmission using appropriate duplexers
or switches and are so labeled only for clarity.
[0047] With reference to FIG. 4, a logical OFDM transmission
architecture is described according to one embodiment. Initially,
the base station controller 10 sends data to be transmitted to
various mobile stations 16 to the base station 12. The base station
12 may use the channel quality indicators ("CQIs") associated with
the mobile stations to schedule the data for transmission as well
as select appropriate coding and modulation for transmitting the
scheduled data. The CQIs may be provided directly by the mobile
stations 16 or determined at the base station 12 based on
information provided by the mobile stations 16. In either case, the
CQI for each mobile station 16 is a function of the degree to which
the channel amplitude (or response) varies across the OFDM
frequency band.
[0048] The scheduled data 44, which is a stream of bits, is
scrambled in a manner reducing the peak-to-average power ratio
associated with the data using data scrambling logic 46. A cyclic
redundancy check ("CRC") for the scrambled data is determined and
appended to the scrambled data using CRC adding logic 48. Next,
channel coding is performed using channel encoder logic 50 to
effectively add redundancy to the data to facilitate recovery and
error correction at the mobile station 16. Again, the channel
coding for a particular mobile station 16 is based on the CQI. The
channel encoder logic 50 uses known Turbo encoding techniques in
one embodiment. The encoded data is then processed by rate matching
logic 52 to compensate for the data expansion associated with
encoding.
[0049] Bit interleaver logic 54 systematically reorders the bits in
the encoded data to minimize the loss of consecutive data bits. The
resultant data bits are systematically mapped into corresponding
symbols depending on the chosen baseband modulation by mapping
logic 56. Preferably, Quadrature Amplitude Modulation ("QAM") or
Quadrature Phase Shift Key ("QPSK") modulation is used. The degree
of modulation is preferably chosen based on the CQI for the
particular mobile station. The symbols may be systematically
reordered to further bolster the immunity of the transmitted signal
to periodic data loss caused by frequency selective fading using
symbol interleaver logic 58.
[0050] At this point, groups of bits have been mapped into symbols
representing locations in an amplitude and phase constellation.
When spatial diversity is desired, blocks of symbols are then
processed by space-time block code ("STC") encoder logic 60, which
modifies the symbols in a fashion making the transmitted signals
more resistant to interference and more readily decoded at a mobile
station 16. The STC encoder logic 60 will process the incoming
symbols and provide n outputs corresponding to the number of
transmit antennas 28 for the base station 12. The control system 20
and/or baseband processor 22 will provide a mapping control signal
to control STC encoding. At this point, assume the symbols for the
n outputs are representative of the data to be transmitted and
capable of being recovered by the mobile station 16. See A. F.
Naguib, N. Seshadri, and A. R. Calderbank, "Applications of
space-time codes and interference suppression for high capacity and
high data rate wireless systems," Thirty-Second Asilomar Conference
on Signals, Systems & Computers, Volume 2, pp. 1803-1810, 1998,
which is incorporated herein by reference in its entirety.
[0051] For the present example, assume the base station 12 has two
antennas 28 (n=2) and the STC encoder logic 60 provides two output
streams of symbols. Accordingly, each of the symbol streams output
by the STC encoder logic 60 is sent to a corresponding IFFT
processor 62, illustrated separately for ease of understanding.
Those skilled in the art will recognize that one or more processors
may be used to provide such digital signal processing, alone or in
combination with other processing described herein. The IFFT
processors 62 will preferably operate on the respective symbols to
provide an inverse Fourier Transform. The output of the IFFT
processors 62 provides symbols in the time domain. The time domain
symbols are grouped into frames, which are associated with a prefix
by like insertion logic 64. Each of the resultant signals is
up-converted in the digital domain to an intermediate frequency and
converted to an analog signal via the corresponding digital
up-conversion ("DUC") and digital-to-analog (D/A) conversion
circuitry 66. The resultant (analog) signals are then
simultaneously modulated at the desired RF frequency, amplified,
and transmitted via the RF circuitry 68 and antennas 28. Notably,
pilot signals known by the intended mobile station 16 are scattered
among the sub-carriers. The mobile station 16, which is discussed
in detail below, will use the pilot signals for channel
estimation.
[0052] Reference is now made to FIG. 5 to illustrate reception of
the transmitted signals by a mobile station 16. Upon arrival of the
transmitted signals at each of the antennas 40 of the mobile
station 16, the respective signals are demodulated and amplified by
corresponding RF circuitry 70. For the sake of conciseness and
clarity, only one of the receive paths is described and illustrated
in detail, it being understood that a receive path exists for each
antenna 40. Analog-to-digital ("A/D") converter and down-conversion
circuitry 72 digitizes and downconverts the analog signal for
digital processing. The resultant digitized signal may be used by
automatic gain control circuitry ("AGC") 74 to control the gain of
the amplifiers in the RF circuitry 70 based on the received signal
level.
[0053] Initially, the digitized signal is provided to
synchronization logic 76, which includes coarse synchronization
logic 78, which buffers several OFDM symbols and calculates an
auto-correlation between the two successive OFDM symbols. A
resultant time index corresponding to the maximum of the
correlation result determines a fine synchronization search window,
which is used by fine synchronization logic 80 to determine a
precise framing starting position based on the headers. The output
of the fine synchronization logic 80 facilitates frame acquisition
by frame alignment logic 84. Proper framing alignment is important
so that subsequent FFT processing provides an accurate conversion
from the time to the frequency domain. The fine synchronization
algorithm is based on the correlation between the received pilot
signals carried by the headers and a local copy of the known pilot
data. Once frame alignment acquisition occurs, the prefix of the
OFDM symbol is removed with prefix removal logic 86 and resultant
samples are sent to frequency offset correction logic 88, which
compensates for the system frequency offset caused by the unmatched
local oscillators in the transmitter and the receiver. Preferably,
the synchronization logic 76 includes frequency offset and clock
estimation logic 82, which is based on the headers to help estimate
such effects on the transmitted signal and provide those
estimations to the correction logic 88 to properly process OFDM
symbols.
[0054] At this point, the OFDM symbols in the time domain are ready
for conversion to the frequency domain using FFT processing logic
90. The results are frequency domain symbols, which are sent to
processing logic 92. The processing logic 92 extracts the scattered
pilot signal using scattered pilot extraction logic 94, determines
a channel estimate based on the extracted pilot signal using
channel estimation logic 96, and provides channel responses for all
sub-carriers using channel reconstruction logic 98. In order to
determine a channel response for each of the sub-carriers, the
pilot signal is essentially multiple pilot symbols that are
scattered among the data symbols throughout the OFDM sub-carriers
in a known pattern in both time and frequency. FIG. 6 illustrates
an exemplary scattering of pilot symbols among available
sub-carriers over a given time and frequency plot in an OFDM
environment. Referring again to FIG. 5, the processing logic
compares the received pilot symbols with the pilot symbols that are
expected in certain sub-carriers at certain times to determine a
channel response for the sub-carriers in which pilot symbols were
transmitted. The results are interpolated to estimate a channel
response for most, if not all, of the remaining sub-carriers for
which pilot symbols were not provided. The actual and interpolated
channel responses are used to estimate an overall channel response,
which includes the channel responses for most, if not all, of the
sub-carriers in the OFDM channel.
[0055] The frequency domain symbols and channel reconstruction
information, which are derived from the channel responses for each
receive path are provided to an STC decoder 100, which provides STC
decoding on both received paths to recover the transmitted symbols.
The channel reconstruction information provides equalization
information to the STC decoder 100 sufficient to remove the effects
of the transmission channel when processing the respective
frequency domain symbols
[0056] The recovered symbols are placed back in order using symbol
de-interleaver logic 102, which corresponds to the symbol
interleaver logic 58 of the transmitter. The de-interleaved symbols
are then demodulated or de-mapped to a corresponding bitstream
using de-mapping logic 104. The bits are then de-interleaved using
bit de-interleaver logic 106, which corresponds to the bit
interleaver logic 54 of the transmitter architecture. The
de-interleaved bits are then processed by rate de-matching logic
108 and presented to channel decoder logic 110 to recover the
initially scrambled data and the CRC checksum. Accordingly, CRC
logic 112 removes the CRC checksum, checks the scrambled data in
traditional fashion, and provides it to the de-scrambling logic 114
for de-scrambling using the known base station de-scrambling code
to recover the originally transmitted data 116.
[0057] Architecture
[0058] The present invention provides a method and system to extend
the architecture of existing wireless communication systems, i.e.
those implemented under IEEE 802.16j to support topology-related
enhancements. These enhancements include but are not limited to
active path and redundant path selection to enhance reliability
support, topology learning and congestion control. Each are
described in detail below. Such enhancements are implemented using
a number of different architectures that include relay stations.
For example, referring to FIG. 7, relay stations 14 and base
station 12 can be implemented in a flat architecture in which all
relay nodes 14 perform the same open systems interconnect ("OSI")
physical layer 1 and media access control ("MAC") layer 2
functions. Of note, many of the figures herein show one or more
relay nodes 14 in communication with base station 12. It is
understood that, although not shown, mobile stations 16 are in
communication with a base station 12 either directly or via one or
more relay nodes 14. In other words, for the sake of simplicity,
many drawing figures do not show mobile stations 16 because the
present invention is concerned with the topology and communication
among relay nodes 14 for communication with the serving base
station 12.
[0059] A different but related architecture is shown in FIG. 8 in
which relay nodes 14 are in communication with base station 12
using a topology that is physically the same as the topology shown
in FIG. 7, but where relay nodes 14 and base station 12 are
arranged in a hierarchical structure. In this arrangement master
relay node 14 performs more functions than a normal relay node 14
in order to distribute some of the complex functions performed by
base station 12 to relay nodes 14. As shown in FIG. 8, master relay
node 14 includes the OSI physical layer 1 and MAC layer 2 functions
as well as some OSI network layer 3 functions. For example,
encryption functions historically performed by base station 12 can
be pushed to master relay node 14 to create communication regions
124a and 124b.
[0060] With the architectures of FIG. 7 and FIG. 8 in mind, the
specific topology enhancements of the present invention noted above
are now described in detail.
[0061] Active Path and Redundant Path Selection
[0062] Active Path and Redundant Path Selection involves the
selection of an initial path through relay nodes 14 to base station
12 as well as the updating of the communication path through relay
nodes 14 as may occur when a relay node 14 is added to or removed
from system 10. The implementation of active and redundant path
selection enhances reliability through the establishment of
multiple communication paths through the network of relay nodes 14
but the use of only a single path at a time.
[0063] Active and redundant path selection can be based, for
example, on the tree topology of networks implemented using IEEE
802.16j standard. However, the definition of the path through relay
nodes 14 can be simplified as compared with other standards such as
the IEEE 802.11s standard, since the ends of the path include a
base station 12 and relay node 14 (wireless communication from
relay node 14 to mobile station 16 is beyond the scope of the
present invention and is not discussed herein).
[0064] In general, in accordance with the present invention, each
relay node 14 selects, or is requested to select by corresponding
serving base station 12 or a master relay node 14, one relay node
14 among its neighbor relay nodes 14 as its parent relay node 14,
and one relay node 14 as its candidate relay node. Neighbor relay
nodes 14 refer to those relay nodes 14 for which a radio link can
be established. This arrangement is explained with reference to the
relay node path diagram of FIG. 9. As is shown in FIG. 9, assume
that a path optimization algorithm (the algorithms for determining
a path to a network are known and are beyond the scope of the
present invention) establishes the primary active path 126 as the
active path from base station 12 to relay node A 14a. In this case,
if relay node A 14a selects relay B 14b as its parent node relay
node B 14b is the access relay node for relay node A 14a. In other
words, the active path is the combination of the link between the
ultimate relay node 14 (relay node 14a) and its parent relay node
(relay node B 14b) plus the path of the parent relay node for relay
node B 14b and so on.
[0065] The redundant path of a relay node is a combination of the
link between relay node 14 and the candidate relay node 14 plus the
path to the candidate relay node 14 from base station 12. For
example, FIG. 9 fills redundant path 128 from base station 12 to
relay node A 14a via candidate relay node C 14c. Of note, relay
nodes having reference designators 14 that include a trailing
alphabetic character, e.g. relay node A 14a, relay node B 14b,
etc., are referred to collectively as relay nodes 14.
[0066] FIG. 9 also shows the tree topology for relay nodes 14 in
which solid lines connecting relay nodes 14 and relay nodes 14 to
base station 12 that are a part of the active tree as shown as
solid lines while links among neighbor relay nodes that are not
part of the active tree are shown as finely dashed lines.
[0067] Under existing standards, a relay node 14 can only have one
parent. However, where there is diversity, a relay node 14 has
multiple parents. Such may occur, for example when a relay node is
in motion and is in soft handoff. In such a case, if the main
parent relay node is thought of as an anchor, the tree structure
can still be preserved and the diversity is reflected by path
definition. The present invention provides two options for path
definition, namely path definition by an equivalent path and path
definition by a primary and assisted path arrangement. Each are
discussed as follows.
[0068] Equivalent path definition is explained with reference to
the relay node topology diagrams of FIGS. 10 and 11. FIG. 10 shows
primary path 126 between base station 12 and relay node B 14b and
alternate redundant path 128 between base station 12 and relay node
B 14b via relay node A 14a. Because the two paths share the same
end points, the primary path 126 and redundant path 128 are
equivalent to a single combined path, shown as equivalent path 130
on FIG. 11. The path capacity, i.e. throughput, of the equivalent
path can be defined as the effective data rate viewed from end
relay node B 14b. In this case, those aspects of the wireless
communication that need to refer to a tree structure can do so by
considering the equivalent path only.
[0069] Diversity can also be reflected by a path definition
arrangement that includes a primary path and one or more assistant
paths. This arrangement is shown in the primary/assistant path
relay node topology diagram of FIG. 12. Under this arrangement, the
primary path is the path along parent relay nodes 14 mainly for
resource assignment control signaling. For example, the parent,
i.e. anchor, node for relay node 14d is relay node 14b. The parent
node for relay 14b is relay node 14a. The primary path is shown in
FIG. 12 as primary path 132.
[0070] The assistant path is the path along non-anchor stations and
is not visible to the effected relay node. For example, an
assistant path between base station 12 and relay node D14d is shown
as assistant path 134 and includes a path using relay node C 14c.
The use of assistant path 134 is on a best effort basis and can be
controlled by a multi-path diversity controller. Although not
shown, it is contemplated that a multi-path diversity controller
can be implemented as part of base station 12, a relay node 14 or a
separate computing device (not shown) that is in electronic
communication with base station 12 and relay nodes 14. Referring to
FIG. 12, if only the primary path is considered, the tree structure
used to support arrangements under existing wireless communication
standards such as the IEEE 802.16j standard is maintained. In other
words, the present arrangement shown in FIGS. 11 and 12 allows for
backward compatibility with existing networks and standards while
providing the additional functionality described herein.
[0071] Relay node path selection is now described. As used herein,
the term "relay node path selection" refers to the selection of a
path between a serving base station 12 through its associated relay
nodes 14 to a destination relay node 14. Path selection includes
two parts, namely initial path selection and path updating. Initial
path selection occurs as a relay node 14 enters or reenters the
network. Such relay nodes 14 can be fixed, portable or mobile. Path
updating occurs when a portable or mobile relay node 14 is handed
over from one base station 12 or relay node 14 to another. Path
updating can also occur as the cell topology changes such as when a
new relay node 14 is added or removed from system 10. In this case,
other neighbor relay nodes 14 may need to reselect a path by taking
the new relay node 14 into consideration due to the topology
change. Path updating may also occur when the quality of the
current path is degraded whether due to congestion, noise, etc.
[0072] Relay node path selection also involves the definition and
implementation of a path selection policy with respect to the
consideration of path selection policy factors that impact path
selection and how to output the path selection. Factors that impact
path selection include limitations on the number of hops through
the network, i.e. a delay requirement, link quality, link capacity,
as well as path capacity requirements. Path selection output with
respect to path selection policy refers to the means by which
active path and redundant path information is output.
[0073] It is contemplated that the determined and defined path can
be symmetric with respect to communication in the uplink (mobile
station 16 to base station 12) and downlink (base station 12 to
mobile station 16) directions or can be asymmetric in the uplink
and downlink directions. The path selection can be determined
purely by base station 12, relay nodes 14 or a combination of relay
node 14 and base station 12, for example by a completely
distributed arrangement or one which is partially distributed in
which a master relay node 14 works in conjunction with a base
station 12 to determine the path.
[0074] Preambles are included in wireless communication frames to
facilitate radio environment measurement by relay nodes 14 for
relay node path selection as well as synchronization among relay
nodes 14. The present invention provides an arrangement to
facilitate preamble transmission by relay nodes 14, referred to as
a relay node preamble, without interrupting other uses of the
preamble, for example cell selection by mobile stations 16 such as
are implemented in IEEE 802.16e wireless communication networks. In
other words, the present invention provides a relay node preamble
arrangement which maintains backward compatibility with mobile
stations 16 to allow mobile stations 16 to communication with relay
nodes 14 in the same manner that IEEE 802.16e mobile stations 16
would communicate with a serving base station 12.
[0075] In accordance with the present invention, a relay node
preamble is periodically transmitted, for example every N 802.16e
frames, by relay nodes 14 after entering the network. This relay
node preamble is transmitted within an uplink or downlink frame,
for example, an IEEE 802.16e uplink sub-frame or downlink
sub-frame. Each relay node's preamble pseudo noise ("PN") sequence
may be the same as assigned to the preamble or may be different.
The retransmission and receipt of the relay node preamble is
synchronized so that at the transmission time for the relay node
preamble, only one relay node is receiving and all others are
transmitting to ensure that the measurement yields a reasonable
result. Put another way, if a relay node 14 is transmitting, it
cannot simultaneously measure and receive the relay node preamble.
It is contemplated that the relay node preamble can be transmitted
on a common channel for multiple-carrier enabled and common-channel
defined networks. It is also contemplated that relay node preamble
reuse within a cell is possible. In such a case, a limited number
of PN symbols are available, but transmission is limited so that
the preamble can be reused in other areas.
[0076] As noted above, if a relay node 14 is configured to be a
serving station, that is to deliver and collect traffic to and from
mobile stations 16 (during normal operation), the relay node 14
transmits a preamble, such as an IEEE 802.16e preamble, to
facilitate cell selection by mobile station 16. However, at the
same time due to radio link changes and removal and addition of
relay nodes 14, relay nodes 14 continuously monitor their radio
environments for purpose of path selection. While one might
consider using existing preambles, such as those defined under IEEE
802.16e for such a purpose, this arrangement does not work because
when a relay node 14 monitors 802.16 preambles, it must stop its
own 802.16 preamble transmission, thereby interfering with the
normal operation of mobile stations 16.
[0077] A relay node preamble implemented in accordance with the
principles of the present invention is transmitted every N frames,
referred to as a relay node preamble cycle. The parameters for the
relay node preamble, e.g., index, PN sequence, etc. may be the same
as an 802.16e preamble for a relay node 14 that is configured to
support 802.16 preamble transmission. However, by using a relay
node preamble in accordance with the present invention, a relay
node does not need to stop its 802.16e preamble transmission for
the purpose of its own radio environment measurement.
[0078] In order to obtain a reasonable radio environment
measurement, a perfect operating environment would be arranged such
that at any relay node preamble transmission time only one relay
node is monitoring and all others are transmitting. Thus,
network-wide relay node preamble plans to avoid more than one relay
node monitoring relay node simultaneously, can be used. For
example, each base station 12 can explicitly establish and indicate
the preamble transmission plan to relay nodes 14 associated with
that base station 12. In another case, base stations 12 can
coordinate scheduling with each other. In either case, this
requires extensive synchronization efforts and is difficult to plan
due to the removal and addition and movement of relay nodes and
master relay nodes.
[0079] As such, it is more characteristic that only a small number
of relay node preambles can be detected by a relay node 14. Those
relay nodes 14 whose relay node preambles can be detected by a
relay node 14 may be within a relatively small geographic area
around the transmitting relay node 14. If a time interval is
defined that includes a small number of relay node preamble cycles
and each relay node randomly selects one relay node preamble cycle
within this interval for monitoring relay node preamble
transmission, the possibility that more than one relay node 14
within this small geographic area is monitoring relay node
preambles is very small.
[0080] Relay node preamble transmission constructed in accordance
with the principles of the present invention is explained with
reference to the diagram shown in FIG. 13. In accordance with the
present invention, "M" relay node preamble transmission cycles form
a base, also referred to as a relay node preamble monitoring cycle
selection base, from which a monitoring cycle is randomly selected
by a relay node 14. FIG. 13 shows M=3. In accordance with this
arrangement, a number of parameters are contemplated and
configured. A relay node preamble transmission cycle ("N") defines
the transmission period of the relay node preamble. In other words,
a relay node preamble is transmitted every "N" frames. FIG. 13
shows N=2. The first frame in each cycle is referred to as the
relay node preamble frame, where an OFDM symbol is reserved for
relay node preamble transmission. The relay node preamble
monitoring cycle selection base ("M") defines the number of cycles
within which a relay node randomly selects a cycle and stops its
own relay node preamble transmission to monitor other relay node
preambles in the corresponding relay node preamble frame. This
arrangement avoids the need for system wide synchronization. A base
starting frame offset ("k") identifies the index of the frame which
starts a base period. Thus, a relay node preamble transmission base
starts from a frame indexed as "i" with "i" meeting the formula:
mode(i, M.times.N)=k. Each base includes M.times.N frames and M
cycles. The cycle can be indexed from 0 to M-1. The relay node
preamble OFDM symbol offset within a relay node preamble frame "j"
identifies the OFDM symbol index within the relay node preamble
frame, thereby referring to the first OFDM symbol in the frame.
[0081] In sum, relay node preambles are transmitted in relay node
preamble window 136. The window is randomly selected by each relay
node 14 as to when it will transmit and when it will receive. To do
this, one frame within a cycle is randomly selected during which
the relay node 14 will monitor. The relay node 14 transmits during
the other windows. This arrangement advantageously allows for the
maintenance of synchronization and also to enable ongoing radio
environment measurement to facilitate path updating.
[0082] Where backward IEEE 802.16e compatibility is not required,
the above-described preamble arrangement can be used for both relay
node radio environment measurement and for transmission to mobile
stations 16.
[0083] As discussed above, there are a number of factors that can
be considered for path selection. These include the number of hops,
link quality and path capacity room. With respect to the number of
hops, the number of hops of a relay node 14 is defined as the
number of hops from the serving base station 12 to that relay node
14. After a relay node enters the network, the parameter "num_hop"
of the relay node 14 can be broadcast. Such broadcast can be
accomplished, for example through a modified downlink channel
descriptor ("DCD") MAC message or as a new relay node message, e.g.
("RN_CONF").
[0084] Link quality is defined herein as the carrier interference
to noise ratio ("CINR") or other measurement from a relay node 14
to a neighbor relay node/base station. For example, referring to
FIG. 14, link quality can be measured as the CINR or other
measurement between RN C 14c and base station 12 or RN C 14c and RN
B 14b. In such case, relay node C 14c acquires link quality by
measuring preambles such as IEEE 802.16e preambles at initial
network entry or reentry or, on an ongoing basis, by measuring the
IEEE 802.16e preamble or the relay node preamble, if
implemented.
[0085] Path capacity room refers to the capacity over the entire
path from end to end if a particular path were used, i.e., the
capacity of the most loaded link in the potential path. In such
case, path capacity room is defined as the additional data rate the
path can support, which as noted above, is the minimum capacity
room along the path. Referring to FIG. 14, it is observed that the
link between base station 12 and relay node C 14c not only has the
lowest capacity but also the most used capacity. The result is that
the link capacity with respect to the room available for additional
transmission in the link between base station 12 and relay node C
14c is the smallest. Accordingly, the path capacity room and the
path from base station 12 to relay node A 14a is the unused (blank)
capacity remaining between base station 12 and relay node C 14c.
Data corresponding to the path capacity room parameter can be
broadcast using a modified DCD message or any other message format
used by a relay node 14 for communication.
[0086] Initial relay node path selection is described. It is
contemplated that the present invention can provide relay node path
selection using a non-centralized controlled, i.e. distributed,
approach in which the new relay node 14 makes the path selection or
a centralized approach in which the base station 12 collects
information and makes the path decision. The non-centralized
controlled initial path selection arrangement is considered
first.
[0087] Under the non-centralized approach, a new relay node, i.e.
relay node A 14a measures downlink preambles, such as IEEE 802.16e
preambles. The relay node selects uplink station based on radio
link metrics, i.e., the radio environment. For example, relay node
A 14a might select relay node B 14b based on radio link metrics.
Relay node A monitors relay node B 14b for a new type length value
("TLV") for an IEEE 802.16e DCD or through another suitable
broadcast message. The path selection factors discussed above can
be monitored.
[0088] Neighbor information acquisition can be obtained based on
this broadcast. Under this arrangement, relay node A 14a can
continue to decode the messages using, for example, an IEEE 802.16e
mobile neighbor advertisement ("MOB_NBR_ADV") with a new TLV or a
new relay node message such as an "RS_NBR_ADV" message. Message
formats are discussed above. The message includes information, for
each associated relay node 14, for the path selection factors.
[0089] Relay node A 14a sends a ranging code in the uplink initial
ranging regions and then sends a ranging request using a new TLV,
such as an IEEE 802.16e "RNG-REQ" message with a new TLV to include
this information. In this case, the RNG-REQ message includes the
MAC address of the relay node A 14a or a preassigned relay node id
along with the top M strongest pseudo noise sequence indices.
[0090] In the alternative, neighbor information can be acquired on
demand. This arrangement requires lower overhead than the broadcast
acquisition method discussed above. In this case, relay node B 14b
can send an RNG-REQ with information for the base station 12 (or
relay nodes 14 corresponding to the top M PN indices). For each PN
index, the path selection factors discussed above are included.
[0091] Relay node A 14a determines the path based on a
predetermined algorithm. As noted above, this predermined path
selection algorithm is beyond the scope of the present invention,
being understood that methods for path selection given a set of
path selection factors is known. If relay node A 14a selects relay
node B 14b, relay node A 14a continues communication using relay
node B 14b. If relay node A 14a does not select relay node B 14b,
or selects relay node B 14b as a candidate path, relay node A 14a
will repeat the above selection process using the selected primary
(parent) relay node 14.
[0092] With respect to relay node path selection, it was noted that
new TLVs can be defined in accordance with the present invention.
With respect to the DCD, the new TLV can include the number of hops
and path capacity room and the new TLV in the RNG-REQ message can
include the number of PN indices M as well as the M PN index value.
Of course, the present invention is not limited to such. It is
contemplated that messages and path selection factors other than
those noted and discussed above can be used. It is also
contemplated that not all paths selection factors must be
considered within the path selection algorithm and that one or more
factors can be used depending on the requirements of the system
designers and/or providers.
[0093] Initial relay node path selection using a centralized
approach in which base station 12 collects information and makes
the path decision is described. Under this arrangement, the new
relay node, e.g. relay node A 14a, measures downlink preambles such
as downlink IEEE 802.16 preambles. Relay node A 14a selects a
station, e.g. relay node B 14b, based on radio link metrics. Relay
node A 14a monitors relay B 14b for the transmission of messages
such as IEEE 802.16e DCD or some other suitable relay node
information message. Neighbor information acquisition can be
obtained by broadcast in which relay node A 14a continues to decode
the IEEE 802.16e MOB_NBR-ADV message using a new TLV or a new relay
RN_NBR_ADV message.
[0094] Relay node A 14a can send a ranging code in the uplink
initial ranging region and transmit an IEEE 802.16e RNG-REQ with a
new TLV in which the new TLV includes the relay node MAC address or
preassigned relay node id and the top M strongest PN sequence
indices. Base station 12 determines the path(s) for relay node A
14a and information for the selected path(s) is transmitted to
relay node B 14b through control layer messaging, for example,
using RNG-RSP or REQ-RES messages.
[0095] In addition to initial path selection, it is contemplated
that the present invention can support path updating such as may be
necessitated by a radio link change resulting from handoff in the
case of mobile or relocated relay nodes or link quality
degradation. In the case of updating path selection, relay node A
14a monitors relay node preambles (or IEEE 802.16e preambles) and
records the channel quality. Relay node A 14a sends an update
request message that includes a list of PN indices and the
measurements. In the case where path selection is centralized, base
station 12 receives this information and determines the selected
path. In this case, base station 12 sends a path update message
including the list of base station and/or relay station id's. In a
case where path determination is non-centralized, base station 12
sends a path update message to relay nodes 14 that includes a list
of relay node id's. For each relay node in the update message, one
or more path selection factors are included. In this case, relay
node A 14a determines the selected path and sends a path update
message that includes the relay node (and base station) path
list.
[0096] It is contemplated that existing standards can be modified
to introduce the new messages that include the path selection
factors such as an "RF_path (route) update-REQ" message. It is also
contemplated that an update response message can be added to
existing standards that includes the list of relay node (and base
station) node id's. It is also contemplated that path updating may
be necessitated by a topology change such as where a new relay node
14 is added or an existing relay node 14 is removed. In such case,
base station 12 can broadcast or multicast the topology change to
its associated relay nodes 14. The topology change can be sent to
all associated relay nodes 14 or a subset of relay nodes 14, such
as those that are impacted by change. This can be done by a
topology update message that includes the id, e.g., PN index, of
the relay node to be added or removed as well as a preambled
transmission schedule update. Base station 12 can provide an
updated preamble transmission/monitoring schedule to its associated
relay nodes 14.
[0097] In this case, the impacted relay node, such as relay node A
14a, follows the updated preamble transmission schedule to measure
the channel quality of each of its neighbor relay nodes 14. Relay
node A 14a sends a path update request message with the list of PN
indices and measurements. The new path can then be determined and
broadcast using arrangements described above for centralized and
de-centralized controlled arrangements for path updates caused by
radio link changes.
[0098] Topology Learning
[0099] Topology learning refers to the procedure under which base
station 12 updates its local topology, i.e. route, table within its
cell whenever the local topology changes. Under this arrangement,
base station 12 asks relay nodes 14 to take new channel
measurements to establish performance values for the new topology.
The topology table includes all associated active relay nodes 14,
and for each active relay node 14, the active link established with
its one or multiple neighbor relay nodes 14.
[0100] With respect to the physical topology learning procedure,
when a new relay node 14 enters the network and after the path
selection determination is made, base station 12 updates its
topology table and requests that the path selection update,
discussed above, be undertaken by one or more of the existing relay
nodes 14. When a relay node 14 is to be removed, base station 12
updates its topology table after receiving a relay node power off
request message from a relay node 14. Base station 12 requests the
path selection update procedure discussed above be performed by the
effected relay nodes 14. On the converse side when base station 12
receives a path selection or path update request message with an
updated path selection, base station 12 updates its topology table
accordingly.
[0101] Congestion Control
[0102] Congestion can be caused by a number of factors, including
but not limited to broken links, link capacity degradation and
input traffic having a rate higher than the link throughput
capacity. For intra-cell congestion control, such congestion
control can be controlled by base station 12 or a master relay node
14. In this case, status updates by associated relay nodes 14 are
polled by the base station 12 (or master relay node 14) or
autonomously reported by the associated relay nodes 14. The status
update can include the downlink buffer status for each child relay
node 14, depending requested bandwidth in the uplink for each child
relay node 14 or even a suggested removal of some percentage of
traffic to be forwarded. In response, the base station 12 or master
relay node 14 can request some mobile stations 16 perform handoff
to another relay node 14 or base station 12 by sending an
appropriate message such as an IEEE 802.16e MOB_BSHO-REQ message.
Base station 12 or master relay node 14 may also request that some
relay nodes 14 perform path updating through the transmission of an
appropriate path update message. In the case where existing
communication standards are used, the intra-cell congestion control
messages can be implemented through the introduction of a new TLV.
Congestion can be an event that triggers a switch between the
active path and the redundant path.
[0103] Relay Station MAC Message Format
[0104] A number of MAC messages are described above for
implementing the functions of the present invention. It is
contemplated that relay node-related MAC messages can use a unicast
MAC message format or a broadcast MAC message format, as
appropriate. It is contemplated that existing naming conventions
can be used to describe these messages, such as "RS_XXX-REQ" and
"RS_XXX-RES" message naming for unicast MAC messages and
"RS_XXX-ADV" for broadcast messages where the "XXX" refers to the
specific name of the MAC message and can for example be an 8-bit
message. This arrangement allows the reuse of a message body format
that is currently used for the IEEE 802.16e wireless communication
standard.
[0105] Although reference was made to existing standards such as
the IEEE 802.16e, j and IEEE 802.11s standards, the entirety of all
of which are incorporated herein by reference, it is understood
that the present invention is not limited solely to the use of
these standards and that reference to these standards is made for
the purpose of illustration and explanation, as well as the
understanding that the functions of the present invention can be
implemented by extending the standards as described herein.
[0106] The present invention provides a method and system by which
topology-related aspects of relay node based wireless communication
networks can be enhanced to provide redundant path selection (while
maintaining the appearance of a tree topology for backward
compatibility), including initial path selection and path updating,
as well as physical topology changes and congestion control.
[0107] It will be appreciated by persons skilled in the art that
the present invention is not limited to what has been particularly
shown and described herein above. In addition, unless mention was
made above to the contrary, it should be noted that all of the
accompanying drawings are not to scale. A variety of modifications
and variations are possible in light of the above teachings without
departing from the scope and spirit of the invention, which is
limited only by the following claims.
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